Weighting interferometric data for direct imaging
Weighting interferometric data for direct imaging
复制标题
加权干涉数据以进行直接成像
DOI：
10.1007/s10686-012-9322-1
复制
发表时间：
2013
影响因子：
3
通讯作者：
F. Boone
中科院分区：
文献类型：
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作者：
F. Boone
新一代干涉阵列，如阿塔卡马大毫米/亚毫米阵列(ALMA)，由大量的望远镜组成，其结构针对傅立叶平面(又名)进行了优化。UV平面)覆盖。因此，解决UV平面中的缺失信息变得不那么关键，成像算法可以重新考虑。这种情况正在变得类似于单填充口径望远镜所遇到的情况，以直接的方式成像变得可能。本文提出了一种新的加权方法来获得“伪清洁”图像，而不需要利用先验信息来求解信号源的傅里叶变换。这种方法类似于但不等同于在不同的比例尺上连续应用稳健加权和逐步缩减。其想法是对数据进行加权，以补偿UV平面中自然权重的不完美分布。这种直接成像技术的代价是，最终的点扩散函数(PSF或光束)可能不遵循简单的解析形状，如高斯(但在光学天文学中也是这样)，并且会失去一些灵敏度(但这是干涉测量中的任何成像算法的情况)。引入了两个参数来控制成像质量和灵敏度之间的权衡，即阈值参数和耦合参数。将该方法应用于16、32和50个天线的ALMA模拟观测。正如预期的那样，这种方法在天线更多、配置更紧凑的情况下效率更高，因为UV平面的覆盖范围更完整。采用紧凑配置的50个天线，与灵敏度损失约10%的自然加权相比，内旁瓣(外旁瓣)的幅度可降低约1/gt；6(>；2)，导致旁瓣低于主瓣峰值的1.6%。该方法只需16根天线，在灵敏度损失约10%的情况下，仍可将紧凑结构的内旁瓣降低约2倍。因此，这种方法可以与新一代干涉阵列一起使用，以有效地产生图像，而不依赖于对源的任何假设。产生的图像的动态范围取决于阵列中的望远镜数量、源大小和可接受的灵敏度损失水平。
The new generation interferometric arrays such as the Atacama Large Millimeter/submillimeter Array (ALMA) are composed of a large number of telescopes and their configurations are optimized for Fourier plane (a.k.a. uv-plane) coverage. As a consequence, solving for the missing information in the uv-plane is becoming less critical and the imaging algorithms can be revisited. The situation is getting similar to that encountered with single filled aperture telescopes and it is becoming possible to make images in a direct way. In this article a new weighting method is introduced to obtain “pseudo-clean” images without using prior information to solve for the Fourier transform of the source. This method is similar but not equivalent to the successive application of robust weighting and tapering at different scales. The idea is to weight the data to compensate for the imperfect distribution of natural weights in the uv-plane. The price to pay for this direct imaging technique is that the final point spread function (PSF or beam) may not follow a simple analytical shape such as a Gaussian (but this is also the case in optical astronomy) and some sensitivity is lost (but this is the case with any imaging algorithm in interferometry). Two parameters are introduced to control the trade-off between imaging quality and sensitivity, namely a threshold parameter and a coupling parameter. This method is applied to simulated ALMA observations with 16, 32 and 50 antennas. As expected this method is found to be more efficient with more antennas and for more compact configurations because the uv-plane coverage is more complete. With 50 antennas in compact configuration it is possible to reduce the amplitude of the inner sidelobes (outer sidelobes) by a factor >6 (>2) compared to natural weighting for ~10 % loss in sensitivity, leading to sidelobes lower than 1.6 % of the main lobe peak value. With 16 antennas only, the method can still be used to reduce the inner sidelobes of a compact configuration by a factor >2 for ~10 % loss in sensitivity. This method can therefore be used with the new generation interferometric arrays to efficiently produce images without relying on any assumptions about the sources. The dynamic range of the resulting images depend on the number of telescopes in the array, the source size and the acceptable level of sensitivity loss.